Gas turbine engines include a combustor, wherein fuel is burned in the presence of air. Within the exhaust product of the engine are contained various emissions, some of which are detrimental to the environment. Some of these unwanted emissions include nitrous oxide, typically referred to as NOX, and carbon monoxide. Many states and local governmental groups have placed stringent requirements for limiting such unwanted emissions, and industry is now searching for various ways to meet these stringent requirements. It has been previously known that if enough water injection is introduced into the main combustor domes, NOX can be reduced considerably. For example, if sufficient water is injected, the NOX can be reduced to 8 parts per million, reference 15% oxygen by volume. However, such introduction of adequate amounts of water has been found to substantially increase the generation of carbon monoxide by as much as 150-200 times the normal carbon monoxide effluent, and as much as 900 lbs./hr. of carbon monoxide has been measured as being emitted for a 50 Mega Watt (M.W.) engine system. In addition, the introduction of these large amounts of water also result in a reduction of the combustion efficiency of typically about 2% in the operation of the engine.
Various proposals have been suggested for reducing the carbon monoxide emitted from a combustor operating with large amounts of steam and water. One proposal is a complex system, including hydrogen enrichment of the fuels. Another is to have the hydrogen directly injected into the combustor flame zones. The attempt of these approaches are both to recover the combustor efficiency and also to reduce the effluent carbon monoxide output from the combustor.
Other suggestions are to use selective catalytic reduction devices (SCR). These devices remove the carbon monoxide from the exhaust flow through a chemical process. However, this approach produces ammonia as a by-product. Other catalytic reactors are also being studies taking a different approach such as attempting to remove the carbon monoxide itself. These likewise are expensive and some have yet to be proven effective.
Accordingly, there is need for an efficient method and apparatus for controlling the combustion emissions in a gas turbine engine to reduce both the NOX and the carbon monoxide emissions to acceptable levels.